A. Field of the Invention
The subject matter of the present invention is a method for equipping a foil material with at least one electrically conductive conductor structure, a method for manufacturing a laminate material which has at least two layers made of foil material and at least one electrically conductive conductor structure between the layers made of foil material, as well as foil materials manufactured by means of the method according to the invention and laminate materials having at least one electrically conductive conductor structure. Subject matter of the present invention are also products manufactured with the foil material and laminate material of the invention, such as for example security documents with electrically conductive security features, and such as electronic circuit units having IC-chip and coil for applications such as contactless data carriers in the form of flat material, as well as foil circuit elements which can be formed as a card body of a chip card or can be integrated in a chip card or in any other flat material.
B. Related Art
The contactless data transmission is increasingly gaining in importance, for example for the purposes of checking and controlling goods, for marking goods of the most different kind in order to avoid forgery or theft, and in particular also for electronic ID documents. The data carrier here typically is an IC-chip with antenna. The chip consists of a plurality of electronic components, and the antenna is an electrically conductive layer, typically in the form of a coil. The stored information can be read-out and displayed for example on a display or cause certain mechanical reactions, for example releasing or blocking the access to a certain region of a building. It is desirable to keep the contactless circuit units as small and in particular as flat as possible so that they can be attached in the form of labels to the surface of objects or integrated as inlets in the layer construction of a card, for example of an ID document, or of any other flat object.
Such a circuit unit is known for example from EP 0 756 244 A2. The disclosed circuit unit comprises at least one insulating carrier substrate on which there is located a conducting, flat coil, and an integrated circuit whose connection points are conductively connected with the coil ends directly or via contacts or are capacitively coupled thereto. On the insulating carrier material there are applied coil layers alternately to insulating layers, wherein each insulating layer has at least one passage through which the adjacent coil layers are conductively interconnected, or wherein the adjacent coil layers are capacitively coupled, so that the individual coil layers yield a coil. The coil layers are preferably printed on with a conductive lacquer or are sprayed on using a corresponding mask or are etched out of a conducting coating located on the carrier material. Other known manufacturing methods are, for example, applying the coil in the form of an electrically conductive coating through a hot stamping method to the carrier material, or punching out the coil of a metal foil or an electrically conductive coated plastic foil and applying it to the carrier material.
A preferred method for manufacturing coil layers and other conductor structures is an etch-free screen printing method, wherein a printing paste with a conducting material is printed on. After the printing, the carrier material is subjected to a heat treatment, in order to remove volatile components of the printing paste.
It is also often desired to activate or to deactivate, i.e. to switch on and off, electronic functional elements, such as chip modules. For this purpose, foil switching elements or foil push-buttons are known. For manufacturing a foil switching element, several foil layers, between which a switching contact is to be established, are put one on top of the other and glued to each other. Here, between two electrically conductive switching foils (contact foils) there is arranged a perforated and electrically insulating intermediate foil, which serves as a spacer and prevents the contact foils from touching each other in the resting state of the foil switching element. The intermediate foil thus effects that the foil switching element is open in the resting state. Through the exertion of pressure on at least one of the two contact foils in the region of the perforation of the intermediate foil, the contact foil is deformed and an electrical contact is established between the two contact foils. If no more pressure is exerted, the contact foil takes on again its original form, as a result of its elasticity. Thereby, the electrical contact between the two contact foils is interrupted. The foil switching element therefore closes the conductor circuit only during the exertion of a pressure on at least one of the two contact foils and opens it upon decrease of the pressure.
The contact between the switching foils of the “switch” and the connection of the switch to the functional elements is established through electrically conductive conductor structures. These structures can be produced in the same way as the above-mentioned flat coils, the production by printing technology being preferred.
Particularly preferably, for the manufacturing of the conductor structures, such as conductor paths, conductive areas and contact areas, pastes with metallic particles are employed, for example silver conductive pastes having silver particles, which are printed on the foils. Here, the problem arises that circuit units and foil switching elements, which are suitable for the integration into chip cards or for foil keyboards or other flat objects, normally consist of plastic foils, that is, the conductor structures must be formed on plastic foils, whereby the foils, moreover, often are thin with thicknesses in the range of about 50 μm to 300 μm. Such plastic foils, however, at higher temperatures are susceptible to distorting, curling and in the worst case shrinking. This property restricts the possibilities of producing flat conductor structures on plastic foils. Structures printed on by means of conductive pastes having metallic particles can only be dried at moderate temperatures, in the case of the usual carrier foils, such as for example PVC and amorphous PVC, at a maximum of 50° C.; polycarbonate, biaxially oriented polyester and paper are suitable for temperatures of about 100° C. The same applies to paper-based materials, as they are employed for security papers and value documents, for example for banknotes. Such value documents often have security features, the check criterion of which is the electrical conductivity. Mostly, it is desired to incorporate the security features in inconspicuous fashion. Manufacturing narrow, flat, inconspicuous conductor structures on or in substrates that are not temperature-resistant, as they are employed for value documents, however, is practically impossible.
At temperatures applicable to usual plastic foils and paper-based foils, there cannot take place a sintering of the metal particles forming the conductor structures. The result is a poor electrical conductivity in comparison to solid metallic conductor structures and a high metal consumption, in order to achieve an acceptable conductivity. Since the conductor structures are manufactured preferably with precious metals, such as silver, a high metal consumption simultaneously causes high costs. Furthermore, relatively high conductor structure thicknesses are required. Nevertheless, the achieved electrical conductivities still need to be improved. With silver conductive pastes there can be achieved values of at best about 1/10 of the conductivity of solid silver, typically much less, about 1/20 of the conductivity of solid silver.
Therefore, there is a need of an improved method for producing electrical conductor structures on foil materials, in particular for producing electrical conductor structures for electronic circuit units and other elements having electrically conductive conductor structures, which elements are integratable in flat materials, such as chip cards.